The present invention relates to the art of oil wellhead isolation tools and in particular to a device for inserting into the wellhead a mandrel which is typically provided with a wellhead isolation nipple assembly, when a particular wellhead is to be serviced. The seal of the nipple engages the inner wall of the casing of the well so that the flow of gas or oil from the casing passes through the mandrel. Likewise, the mandrel allows the injection of sealing substances through the mandrel into the casing. The upper end of the mandrel is provided with a valve which serves the purpose of selectively opening or closing the passage through the mandrel.
The inserting of the sealing nipple in the casing has so far been accomplished by a mechanism using a series of two or more hydraulic cylinders the cylinder casings of which are fixedly secured to the ends of a transverse beam, usually an upper beam, while the piston rods are secured to the ends of a transverse second, lower beam.
The central part of the upper beam is fixedly secured to the upper end of the mandrel so that, upon contraction of the cylinders at both sides, the upper beam pushes the mandrel into an oil well casing. The hydraulic mechanism replaced previously used purely mechanical devices such as a plurality of rack and pinion devices similarly connected to the respective beams. These devices were complex in structure and bulky. There were problems with the jamming of the device as it was difficult to maintain a permanently balanced operation of several displacement means, each transversely spaced a distance from the axis of the mandrel.
The hydraulic cylinders presented an improvement in that relatively high displacement forces could be generated. However, the overall arrangement is still bulky and the jamming remains a problem.
Accordingly, it is an object of the invention to further advance the art of the wellhead isolation tools by simplifying the structure while at the same time virtually eliminating the possibility of the jamming of the tool during the inserting or withdrawal of the mandrel into and out of the respective casing.